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    Achievement of Exceptionally High Mobilities in Modulation Doped Ga sub (1-x) In sub x As On InP Using a Composite Channel with x = 0.75 and 0.25

Achievement of Exceptionally High Mobilities in Modulation Doped Ga sub (1-x) In sub x As On InP Using a Composite Channel with x = 0.75 and 0.25

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Increasing the InAs mole fraction in this Ga sub (1-x) In sub x As layers on InP beyond the lattice matched value of x = 0.53 has been shown conclusively in recent years to yield superior materials for high performance FETs. Higher x values are associated with smaller electron effective mass, higher electron mobility, and higher peak electron velocity. For n-type structure, they provide the benefit of higher conduction band discontinuity against Al sub (1-y) In sub y As. For p-type structure, they offer strain splitting of the valence band with light hole conduction in the plane. Both the highest room-temperature mobility in a modulation doped structure and the highest cutoff frequency in an FET today owe their success to this type of pseudomorphic structures grown by MBE.